Main areas of investigation in our laboratory concern a) the regulation of branched chain amino acid catabolism, and b) the regulation of muscle protein turnover. The two areas of investigation are interrelated through the demonstrated effects of the branched chain amino acids, particularly leucine, in promoting protein synthesis and inhibiting protein degradation in skeletal and heart muscle. The role of hormones, metabolic intermediates and the redox potential in regulating branched chain amino acid catabolism will be investigated, with special emphasis on changes associated with fasting and insulin-deficient diabetes. Studies concerning the regulation of the branched chain keto acid dehydrogenase complex in liver and muscle will be continued. We recently presented evidence for post-transcriptional control of muscle protein synthesis by the cytosolic redox potential. Studies will be continued to delineate the mechanisms whereby three apparently independent factors, i.e., insulin, leucine and the cytosolic redox potential modulate muscle protein synthesis at the level of translation.